The invention relates to robot systems. It finds particular application in conjunction with a system and method for allocating mapping, localization, planning, control and task performance functions in a sentry robot system and will be described with particular reference thereto. However, it is to be appreciated that the invention is also amenable to other applications.
Mobile robots have been designed, developed and deployed to handle a variety of tasks such as cleaning and security. Most mobile robots are non-autonomous; that is, they are unable to autonomously navigate. The economic benefits provided by non-autonomous robots are limited by the inflexible behavior of the robots and their extensive installation costs. Skilled technicians often must be hired and paid to preprogram the robots for specific routes and tasks. It may be necessary to install objects in the environment to guide the robots, such as tracks, buried signal emitting wires, markers or sensors. Further modifications to the environment may also be necessary to minimize installation and operational problems.
Some mobile non-autonomous robots can detect obstacles blocking their paths, and can stop or deviate slightly from their paths to avoid such obstacles. If the environment is modified significantly, however, such as by moving a large item of furniture, conventional non-autonomous robots do not properly react. Part or all of the installation process often must be repeated. Given this limitation, non-autonomous robots are usually deployed only on stable and high value routes. Though some non-autonomous robots rely on random motion to perform their tasks, such as pool cleaning robots, only a limited number of applications are amenable to this approach.
Fully autonomous mobile robots have begun to emerge from research laboratories during the past few years. Autonomous robots are able to navigate through their environment by sensing and reacting to their surroundings and environmental conditions. Autonomous robot navigation involves four primary tasks: mapping, localization, planning and control. These closely related concepts are analogous to asking the questions “Where am I?” (mapping and localization), followed by “Where do I want to be?” or “What do I want to do?” (planning), and finally, “How do I get there?” or “How do I do that?” (control).
Once mapping is complete, the robot's current position, orientation and rate of change within the map must be determined. This process is referred to as localization. Autonomous robots that rely on 2D mapping and localization are often not able to navigate with adequate reliability due to the relative simplicity of the map. Often, the robots become lost, stuck or fall. Use of dynamic 3D mapping and localization, by contrast, permits navigation that is more reliable but involves complex calculations requiring a large amount of computational overhead. 3D maps typically have millions of cells, making straightforward operations such as landmark extraction, localization and planning computationally intensive. The resulting computational delays limit the speed of robot movement and task performance.
Once mapping and localization are accomplished, task planning and performance must be undertaken. Some localization will still be required during task performance. With one robot attempting to localize while performing tasks leads to unacceptable delays. If multiple robots are used, the tradeoffs described above are often still present, and must now be dealt with multiple times over.
Published PCT patent application No. WO 01/38945 A1, now U.S. Pat. No. 6,374,155 to Wallach et al. and assigned to Personal Robotics, Inc., discloses an autonomous mobile robot system that allocates mapping, localization, planning and control functions to at least one navigator robot and allocates task performance functions to one or more functional robots. The at least one navigator robot maps the environment, localizes itself and the functional robots within the map, plans the tasks to be preformed by the at least one functional robot and controls and tracks the at least one functional robot during task performance. The at least one navigator robot performs substantially all calculations for mapping, localization, planning and control for both itself and the functional robots. In one implementation, the at least one navigator robots remains stationary while controlling and moving the at least one functional robot in order to simplify localization calculations. In another embodiment, the at least one navigator robot is equipped with sensors and sensor processing hardware required for these tasks, while the at least one functional robot is not equipped with sensors or hardware employed for these purposes.
In view of the above, a sentry robot system having fast, accurate and cost effective mapping and localization, as well as effective planning and allocation of tasks with improved sensing of the environment is needed.